Question about what happens to density of airflow through a heated tube

I know the basic equations for airflow, but for some reason this question has been puzzling me: say you have a copper tube open at one end and connected to a piston cylinder system at the other. Air is drawn through the copper tube and into the cylinder as the piston moves from top to bottom, and while this is going on you are holding a blowtorch up to a section of the copper tube and thus transferring some heat to the flowing air. Other than increased temperature, how would the air entering the cylinder differ from the exact same experiment minus the blow torch? For some reason this is really bugging me.